Knife sharpener



FIG. 1 is a perspective view of a knife sharpener showing my new design,in an extended state;

FIG. 2 is a front elevational view thereof, the rear appearing the same,in a closed state;

FIG. 3 is a side elevational view of FIG. 2;

FIG. 4 is a top plan view of FIG. 2; and,

FIG. 5 is an alternate perspective view thereof.

The ornamental design for a knife sharpener, as shown.